The present invention relates to the field of producing elements out of composite material. More particularly, the present invention relates to a method of producing tooling for molding a part by resin transfer molding (RTM), and it also relates to tooling produced by the method.
In an RTM process, a textile preform is inserted into a mold cavity of a mold. After the mold has been closed, a thermosetting resin is injected under pressure into the cavity via injection channels. The pressure is maintained in the cavity for a setting period of the resin, during which the temperature is increased in order to encourage such setting. After unmolding, a composite part is thus obtained made of thermoset plastics material that is reinforced by the fibers of the textile preform, having a shape and dimensions that are accurate, and that normally require only a limited amount of post-treatment. The resin transfer molding (RTM) process thus enables composite parts to be mass produced.
During the RTM process, the textile preform may be subjected to high levels of stress. Although simulation means make it possible, to some extent, to evaluate such stresses in advance in order to define a preform that will give rise to the desired molding, it continues to be necessary to pass via a step of validating a preform, for the purpose of checking for any registration errors in the fibers and also their distribution and density in the final molding, and also checking for overall deformation of the molding, ease of shaping the preform, and other production parameters. In order to proceed with such validation by production testing, it is nevertheless necessary to have production tooling for use in the RTM process.
The tooling used for resin transfer molding is similar to that used in conventional injection molding of plastics. It thus comprises a mold, typically made of metal, and having a mold cavity, which normally requires high precision machining with very small tolerances. In addition, in order to enable temperature to vary in the mold cavity as is normally required for setting the resin, heating and indeed cooling means normally need to be arranged in the mold. Consequently, producing such final tooling for validation testing of a preform would take an excessive length of time and would turn out to be very expensive in the event of failure.
Nevertheless, machining simplified preliminary metal tooling in a block of metal presents other drawbacks. A solid metal mold would not make it possible to reproduce the rate of temperature rise desired for the final production tooling. Furthermore, machining such tooling out of a block can consume precious time.